CERAMIC COATING FOR VALVE SEATS AND STEMS BY PLASMA CHEMICAL VAPOR-DEPOSITION

To extend the lifetime of the valve seats and stems used in nuclear power plants, we have developed a unique ceramic coating technique using plasma chemical vapor deposition (CVD). Multilayer coatings of Al2O3/TiN/TiC, Al2O3/TiC and TiN/TiC were deposited onto Stellite and stainless steel substrates. The mechanical and physical properties of the coatings were evaluated by various methods. The coated specimens showed good wear resistance in a high-temperature water environment. Corrosion resistance was evaluated in an autoclave at a temperature of 548 K for 200 h. The coated specimens showed excellent performance in reducing the cobalt level dissolved in the testing solution. The weight loss of the multilayer-coated AISI403 specimen, as evaluated by a cavitation erosion test, was less than 1% of that of the uncoated AISI403. However, for the coated Stellite-padded AISI316L substrate, the weight loss was almost the same as that of the uncoated specimen.